Plastic materials for industrial machinery

Plastics offer a number of advantages for packaging, conveying, and food processing machinery. Plastic materials are significantly lighter than metals, which reduces weight and saves energy costs for moving parts. Additionally, plastics tend to have good sound deadening characteristics, which allows machinery to run quieter. Plastic materials are tough and durable with many engineered to wear well and stand up to cleaning chemicals.

Applications for plastic materials include:

Machine guards

Bearings and bushings

Star wheels

Guide rails

Gears

Chain guides

Flexible tubing

Transparent machine guards

Polycarbonate and acrylic sheet materials are ideal choices for machine guards. They are far more durable than glass and are easy to fabricate and install.

Polycarbonate offers the advantage of superior toughness and impact resistance. Additionally, polycarbonate sheet can be bent into complex shapes using a sheet metal break, which simplifies fabrication since no heating is required.

Acrylic has superior clarity and it is stiffer than polycarbonate. Acrylic is often used for large unsupported machine guards when the impact resistance of polycarbonate is not required.

Both acrylic and polycarbonate are available with hard-coated surfaces that enhance both chemical resistance and scratch resistance.

Plastics for friction and wear applications

Plastics such as UHMW, nylon, and acetal have low friction and outstanding wear characteristics, even in the absence of external lubrication. These materials are widely used in high speed packaging and conveying applications where wear resistance and smooth operation is essential.

UHMW is tough and durable. It performs well in applications such as chute liners and star wheels where low friction and excellent wear performance are required. LubX® CV is a special grade of UHMW with lower friction and superior wear properties compared with standard UHMW.

Acetal (sometimes referred to by the brand name Delrin®) is easy to machine into complex shapes. It has low friction and it has superior strength and stiffness compared with UHMW.

Nylon has outstanding wear characteristics, particularly when it is in contact with metal in dry environments. Nylon is often used for gears, bearings, and bushings, when long wear life is required and external lubrication needs to be avoided.

Semicrystalline PET has strength and stiffness similar to nylon and acetal, however it has superior dimensional stability and stain resistance. It is often specified for tight tolerance food processing machinery applications.

Some plastics such as UHMW, polypropylene, and PTFE have excellent chemical resistance. Other plastic materials like acrylic and polycarbonate have limited chemical resistance. The chemical resistance of plastic will depend on a number of factors including the concentration of the chemical, the part geometry, the stresses on the part, and the operating temperature. Please contact Curbell if you have questions about the chemical resistance of a particular plastic material.

Many unfilled virgin plastic materials including UHMW, acetal, and nylon meet one or more of the FDA's requirements for direct food contact. Please consult with Curbell if you have a specific requirement for compliance with FDA or any other regulating agency.

Plastic materials tend to have much higher rates of thermal expansion than metals, and plastic parts may grow out of tolerance when heated. Additionally, some plastics will swell in the presence of water or other chemicals. Materials with low rates of thermal expansion and low moisture absorption such as semicrystalline PET are often used when tight dimensional tolerances are required.

A number of factors must be considered when selecting plastic materials for high temperature applications. These include the rate of thermal expansion of the material, softening behavior, creep, and the ability of the plastic to resist long-term thermal degradation. Materials such as PPS, PEEK, and PTFE tend to perform well in high temperature applications. Please consult with Curbell if you need help selecting plastic material for use in a high temperature environment.

Generally speaking, semicrystalline thermoplastics such as UHMW, acetal, nylon, and PET tend to have low friction and long wear life. That being said, wear behavior is a complex issue that depends on the composition and smoothness of the mating surface, loads, velocity, and part geometry.